"A favoured familiar"

Your vampire master/mistress has bestowed power upon you as they have taken a liking to or are amused by you and your actions as one of their familiars. The vampire's aims are to use you as an extra set of eyes and ears, a source of entertainment, as well as an external conduit for blood, either your own or another creature's to show your loyalty.

You have the Vampiric Connection trait of the Vampire Familiar creature giving you a constant connection to your patron.

 

Level 3: Vampire's Conduit

Your patron is able to feed off of the necrotic damage you deal as you pull the life force and blood from your foes.

When you damage an enemy that is at half of it's maximum hit points or below, or your damage brings it to half it's hit points or below, you deal an additional number of d4 equal to your proficiency bonus necrotic damage.

At the end of each long rest you must roll a number of d6 equal to your warlock level. The total of the dice is the accumulative necrotic damage you must deal before your next long rest to satiate your patron's hunger. If the total rolled is not met by the next time you long rest you must sacrifice your own blood losing the difference between the total rolled and the necrotic damage you dealt hit points. If you deal more necrotic damage than the total rolled you will gain temporary hit points equal to the excess damage to a cap of 4x warlock level.

Level 3: Vampiric spells:

At the specified warlock level's your patron ensures that you always have the listed spells prepared.

Warlock level:

3: Thaumaturgy, Sleep, Command, Moonbeam, Pass without trace.

5: Bestow curse, Phantom steed.

7: Evard's Black tentacles, Wall of fire.

9: Contagion, Dominate person.

 

Level 6: Forms of the Familiar

Starting at level 6, you can shape-shift into one of the two forms below a number of times equal to your proficiency bonus 1 hour, until you choose to change back to your original form or the form's hit points drop to 0:

Swarm of bats: The swarm of bats will deal a number of d4 necrotic damage equal to your proficiency bonus to any creature that starts its turn occupying the same space as you

Dire wolf: The dire wolf's Bite attack deals an additional number of d6 necrotic damage equal to your proficiency bonus.

You cannot cast spells whilst in these forms. Each form has an additional 4 hit points per warlock level.

Level 10: Deepened bond

Starting at level 10 you gain the following bonuses:

Enhanced deathless agility: You gain an additional 20 feet of movement and the Deathless Agility trait from the Vampire familiar stat block.

Fangs of the conduit: You gain the ability to grow fangs that are linked to your patron. A number of times equal to your proficiency bonus per long rest you can use an action to make a melee spell attack with your fangs dealing 2d12 necrotic damage giving the target disadvantage on their next attack roll or saving throw.

Step of the hunter: Per short rest you can use your bonus action to use half your movement speed to teleport 5 feet behind an creature or an area that is in full darkness within 40 feet of you.

Level 14: Patron's second heart

Starting at level 14 your heart becomes intertwined with your patron, making you a source from which your patron can be brought back from destruction granting you increased access to your patron's power.

You gain the following benefits:

Vampiric agility: You Permanently gain the effects of Spider Climb

Delegated command: Once per short rest you can summon 1d4 Vampire familiar(s) that follow your commands, and if you become unconscious they will defend your body. The Vampire familiar(s) vanish after 1 hour.

Shared syphon: You heal for half the amount rounded down of any bonus necrotic damage dealt by any of this subclass' features.